Character aligning restraints for high speed printers

ABSTRACT

Printing apparatus wherein a webbed medium is intermittently fed from print line to print line between a row of actuatable print hammers and a continuously displacing set of print characters. Between intermittent advances the webbed medium is impacted by selected ones of the print hammers to print a line thereupon, such impact being effective to engage the impacted area of the webbed medium with the continuously moving print characters, thus urging the webbed medium out of a predetermined alignment with the print hammers. Restraining means prevents such shiftable movement by immobilizing the webbed medium in opposition to the undesirable influence of the moving print characters.

Unite States Patent 1 1 Skiba et a1.

1 51 May 15, 1973 CHARACTER ALIGNING RESTRAINTS FOR HIGH SPEED PRINTERS Inventors: Raymond A. Skiba, Detroit; John W. Funk, Dearborn; Eugene L. Merlino, Jr., Dearborn Heights, all of Mich.

Burroughs Corporation, Detroit, Mich.

Filed: Mar. 31, 1971 Appl. No.: 129,853

Assignee:

U.S.Cl. ..101/93 C, 197/133 R Int. Cl ..B4lj 15/00, B41j 1/34 Field of Search ..101/93 C, 91, 288,

References Cited UNITED STATES PATENTS 6/1967 Epstein et al .....226/17 8/1967 Bernard ..197/133 R 12/1968 MIX etal ..197/133R 1/1969 Pitt ..197/133R 3,550,745 12/1970 Bisone ..197/133 R 3,568,812 3/1971 Eitel ..197/133 R FOREIGN PATENTS OR APPLICATIONS 1,022,370 3/1966 Great Britain ..197/133 Primary Examiner-William B. Penn Att0mey- Kenneth L. Miller & Edwin W. Uren [57] ABSTRACT Printing apparatus wherein a webbed medium is intermittently fed from print line to print line between a row of actuatable print hammers and a continuously displacing set of print characters. Between intermittent advances the webbed medium is impacted by selected ones of the print hammers to print a line thereupon, such impact being effective to engage the impacted area of the webbed medium with the continuously moving print characters, thus urging the -webbed medium out of a predetermined alignment with the print hammers. Restraining means prevents such shiftable movement by immobilizing the webbed medium in opposition to the undesirable influence of the moving print characters.

8 Claims, 7 Drawing Figures PATENTEU 51975 3,732,810

' SHEET 1 OF 3 INVENTOR. JOHN W. FUNK MOND SKIB ENE L. MER O,JR.

PATENTED 51875 3.732.810

sum 2 0F 3 JGHQQHIUXJMMOQOHZTUVWXY FIG.4

PATENTEU 5 I973 SHEET 3 or 3 CHARACTER ALIGNING RESTRAINTS FOR HIGH SPEED PRINTERS BACKGROUND OF THE INVENTION This invention relates generally to printing apparatus and more specifically to document aligning means for on-the-fly types of printers.

The subject of present concern is with improving the print quality of so-called on-the-fly line printers. These types of printers usually operate by impacting a medium such as paper against moving sets of print characters carried cyclically past a row of print hammers by such means as a constantly rotating drum or a driven chain formed in an endless loop, the impression of the character being transferred to the paper by inking means interposed between the hammers and the moving characters. Selective actuation of discrete ones of the print hammers prints a desired line of characters across the paper. After each line of selected characters is printed the paper is advanced to the next line.

There are two general aspects of print quality; one of which concerns the quality of the individual characters, i.e., the form of the character and the line quality. The other aspect of print quality concerns the placement of the individual characters with respect to one another and, relatedly, with the placement of one line of print with respect to another line. It is to this latter aspect that the present invention is directed. Accordingly, it is a primary aim of the present invention to improve the quality of the printing in on-the-fly types of line printers.

It is more specifically an object of the present invention to provide a high speed printer with the capability of printing a text of characters in which each character is positioned in exacting relationship to the other characters of the text.

It is another object of the present invention to provide means for improving the registration of individual printed characters that is adaptable to existing high speed printers.

It is further an object of the present invention to accomplish precise character registration by relatively uncomplicated and inexpensive means.

SUMMARY OF THE INVENTION In accordance with the invention and in satisfaction of these and other objects, a printing apparatus is provided having a plurality of actuatable print hammers disposed in a row. A carrier of print characters continuously displaces the print characters through a print station disposed in juxtaposition to impacting ends of the print hammers. A line of print is formed by actuating selected ones of the print hammers to impact a webbed medium such as paper disposed in a predetermined position in the print station against selected ones of the passing print characters. Paper feeding and aligning means stops the advance of the paper during the printing of each line. Forces are imparted to the paper by the impacted ones of the displacing print characters which tend to shift the paper in the displacing direction of the character. Restraining means mounted in proximity to the print station engage the paper to immobilize the paper against the shifting forces of the displacing print characters.

BRIEF DESCRIPTION OF THE DRAWINGS To facilitate a more complete understanding of the invention the following is a detailed description of preferred embodiments thereof described with reference to the drawings in which:

FIG. 1 is a front elevation of a drum printer incorporating the invention;

FIG. 2 is an enlarged side elevation of a portion of the drum printer, partially in cross-section;

FIG. 3 is a perspective view of the solenoid-actuated clamp;

FIG. 4 is a top elevation of a chain printer incorporating the invention;

FIG. 5 is an enlarged side elevation of a portion of the chain printer, partially in cross-section;

FIG. 6 is a side elevation of a drum printer incorporating the invention embodied in a one-way clutch; and

FIG. 7 is a perspective view, partially broken away, showing two one-way clutches mounted on a support bar.

DETAILED DESCRIPTION OF THE INVENTION Turning now to the drawings wherein like reference characters identify identical elements in each of the Figures and particularly to FIGS. 1 and 2 there is shown an on-the-fly, line type of printer, such as that commonly used in computer peripheral applications. A webbed medium such as paper 10 is advanced and guided through a print station 12 by feeding and aligning means, or in the present instance, tractors l4 having studs 16 engaged with marginal perforations 18 in the paper 10.- One set of tractors 14 positioned anteriorly of the print station 12 and another set, positioned posteriorly thereof, synchronously drive the paper 10 intermittently through the print station. During a stop cycle of the intermittent paper drive, a line 20 of characters is imprinted into that area of the paper disposed within the print station 12. After the printing of each line, the tractors 14 advance the paper 10 upwardly, as shown, to the next print line 20.

The print station 12 is formed between a row of actuatable print hammers 22 and sets of raised print characters 24 juxtaposed thereto. The print characters 24 are continuously displaced past the print hammers 22 by a carrier or print drum 26. There is one print hammer 22 in the row associated with each discrete character position in the print line 20 and each print hammer 22 has a corresponding set of characters disposed in a row about the periphery of the print drum 26. To print a line on the paper 10, selected ones of the print hammers 22 are actuated by means such as schematically represented by the block 25 in FIG. 2 to impact the paper against predetermined ones of the by-passing characters 24. Inking means, such as inked ribbon 27 is disposed between the print hammers 22 and the drum 26 to create a readable impression on the paper 10 when it is pressed against a raised character 24 on the print drum.

Printing apparatus of this general type are capable of printing in excess of 1,000 lines per minute. Such high printing rates require that the raised print characters 24 be displaced through the print station 12 with a continuous motion at relatively high velocities. The effect of a great number of print hammers 22 impressing the paper 10 against the displacing print characters 24 is to urge the impacted areas of the paper in the direction of character movement. Since the paper 10 is slightly flexible and the engagement of the marginal perforations 18 by the studs 16 of the tractor 14 allows some play,

this urging force of the displacing character nonuniformly moves the paper out of proper registration for the printing of successive characters in the same print line. The misalignment of characters resulting from this effect may be observed in Appendix A( l By incorporating a frictional restraining means or in the present instance, a solenoid actuated clamp 28 to positively immobilize the paper in close proximity to the print station 12, the misaligning effect of the moving characters 24 may be counteracted. A plurality of clamps 28 are disposed on a line parallel to the rotational axis of the print drum 26 and in close proximity to the print station 12. As shown in FIGS. 2 and 3, pivotal lever arm 30 of each clamp 28 serves as a mount for resilient pads 32 composed of a material having a high coefficient of friction with the webbed medium or paper 10. The resilient pads 32 are biased into pressing engagement with the paper 10 by a biasing member or compression spring 34. The paper 10 is borne upwardly in opposition to the downward pressure of the resilient pads 32 by a bearing surface 36. One end of the compression spring 34 is fixed to a supporting frame 38 and the other to an upper surface of the lever arm 30. The supporting frame 38 also serves to pivotally mount the lever arm 30 and to rigidly position a solenoid 40 so that one pole 42 thereof extends into close proximity with the upper face of the lever arm 30. Energizing the solenoid 40 thus effects a retraction of the lever arm 30 and resilient pad in opposition to the biasing force of the compression spring 34.

Supported on a rigid bar 44 transversely across the paper 10 the clamps 28 are spring-actuated and solenoid-deactuated to respectively lower and raise the resilient pads 32 into and from engagement with the paper. Deactivation the clamps is precisely timed with the paper movement so that the resilient pads 32 are retracted from the paper 10 at the instant before the paper begins to advance. Similarly, the actuation of each clamp 28 is precisely timed so that the resilient pads 32 engage the paper 10 simultaneously with the paper being halted by the tractors 14. It will be recognized that the energizing of the solenoids must be initiated a predetermined time before the paper It) begins to advance so that the delay arising from the build-up of the magnetic field of the solenoid and with the pivotal displacement of the lever arm 30 are taken into account. Similarly, the solenoid 40 must be de-energized at a predetermined time before the paper 10 is stopped. With the paper 10 held motionless by the resilient pad 32 during the printing of each line 20, a remarkable improvement in the positioning of the characters within the line has been achieved. This improvement may be illustrated by comparing the uniformity of character positions in the print line of Appendix A(l) with those of Appendix A(2), the latter being an example of the print quality achieved by the same drum printer, but with the actuated clamps 28 described above being incorporated therein.

The problem of nonuniformity of character alignment that has engendered the creation of the improved printing apparatus hereinbefore described is common to most so-called on-the-fly, line printers. A chain printer, such as illustrated in FIGS. 4 and 5 for example, presents a variation of the problem in that the print characters are continuously displaced through the print station in a direction parallel with the print line, whereas, with the drum printer the print characters 24 are displaced at right angles to the print line 20. In the illustrated type of chain printer a webbed medium or paper 46 with marginal perforations 48 is intermittently I advanced through a print station by a set of laterally spaced tractors 50 disposed posteriorly of a print station 52. Print characters 54 are carried and displaced by an endless belt 55 in juxtaposition to and along a row of actuatable print hammers 56 disposed on the other side of the paper 46 from the displacing characters 54. When a hammer 56 impacts the paper 46 against a selected character 54 on the continuously moving belt 55, the paper is urged by that displacing character in the direction of its movement, or horizontally with respect to the print line 58. Such urging forces being nonuniform, deviations in horizontal spacing of the characters result. Further, the displacing influence of the moving characters 54 urging the paper 46 in the direction of movement tends to pivot the paper unevenly about the laterally opposed tractors 50. With the characters 54 moving past the print hammers 56 from right to left, as shown, there is a tendency for the paper 46 to pivot slightly about the right-most tractor 50 thus tending to raise the left hand side of the paper and lower the right hand side. An example of the printed text of an unimproved chain printer, such as heretofore described, may be seen in Appendix 8(1) where nonuniform spacing may be observed between pairs of printed characters.

When a plurality of solenoid actuated clamps 28 such as those described above in connection with the drum printer are operably employed with the chain printer, as shown in FIGS. 4 and 5, the misalignment problems of the unimproved printer are substantially overcome. An example of the printed text of a chain printer incor porating the solenoid activated clamps 28 may be seen in Appendix 8(2).

The configuration and the operation of the solenoid actuated clamps 28 are substantially the same with the chain printer as with the drum printer. Like with the drum printer, the resilient pads 32 are biased by compression springs 34 to immobilize the paper 46 against a bearing surface 60. When the tractors 50 begin to advance the paper 46 the solenoids 40 are energized and the lever arm 30 that mount the resilient pads 32 are retracted from engagement with the paper in opposition to the biasing face of the compression spring 34. An additional feature of the actuatable clamps 28 in the chain printer embodiment is the provision of a paper tensioning skid 62 which rides upon the surface of the paper 46 at all times to tension the paper in slidable opposition to the driving influence of the tractors 50. An important effect of the paper tensioning skid 62 is to prevent slight overruns caused by the inertia of the paper 46 during the deceleration phase of the intermittent drive.

Means to restrain the paper in opposition to the misaligning influences of the continuously moving characters have thus far been described in terms of one embodiment, specifically, the solenoid actuated clamp 28. Good results may also be obtained with alternative devices. ln on-the-fly types of printers where print characters are moved through the print station at substantially right angles with the print line, restraining means which have the characteristic of restraining paper motion in one direction while permitting it in the other may be used. One of such restraining means is a one-way clutch such as illustrated in FIGS. 6 and 7. Positioned posteriorly of a print station 64 in a printing apparatus where raised print characters 66 are displaced through the print station in the direction opposite of paper advancement, a one-way clutch, such as at 67, serves to restrain rearward motion of the paper 68, such as would be imparted thereto by the action of print hammers 70 impressing the paper 68 against ones of the displacing characters 66. During paper advancement however, the one-way clutch merely rides on the paper presenting no significant drag to the advancement thereof.

The exemplary one-way clutch 67 is one of a common variety of such clutches having as one of its elements an annular cylinder 72 with a periphery 74 composed of a material having a high coefficient of friction with the webbed medium or paper 68. The annular cylinder 72 is freely rotatable in one direction about an axial shaft 76. Means such as constrictor rollers or a ratchet arrangement (neither shown) couple the axial shaft 76 and the annular cylinder 72 to brake the rotation of the annular cylinder about the axial shaft in the other rotational direction. The axial shaft 76 is journaled for rotation in a mounting bracket 78. The bracket is pivotally connected to a standard 80 and biased in a first pivotal direction by a compression spring 82 compressably interposed between the bracket and a finger 84 of the standard 80. A plurality of one-way clutches 67 are supported transversely across the paper 68 in close proximity to the print station 64 by a mounting bar 86 disposed posteriorly of the print station 64 of a drum printer. The periphery 74 of the annular cylinder 72 of each one-way clutch 67 rides upon one face of the paper 68, the other face of the paper being borne Appendix A, DRUM PRINTER (1) Without Clamp 0123456769Q123456789 o1234567a9 12a45era9 With Clamp oizsasarse O123456TB90123456TB9Q123456789 o1234S6TB9 2345W89 0123456789o1234S6T890123456789 0123456789 0123456789 23456769 23456789 g3456769 23([567890123456789 mswse aasorw 3a$6769 234567B9 in opposition to the pressing force of the one-way clutch 67 by a bearing surface 88. The normal force applied by the periphery 74 of the annular cylinder 72 to the paper 68 must create a frictional restraint sufficient to hold the paper motionless in opposition to the printing forces but of not such great magnitude as to cast an impression of the periphery 74 on lower documents of multisheet, carbon duplicating types of webbed medium.

While the invention has been described in terms of twopreferred embodiments, there are other alternatives and modifications that may be apparent to one skilled in the art in light of the foregoing description. It is intended therefore to include within the appended claims all such alternatives andmodifications that do not truly depart from the inventive concept disclosed herein.

Further appended hereto are two groups of printed texts illustrating the improvement in print quality obtained using the present invention. A first of the two groups, Appendix A, facilitates a comparison of the print quality obtained from an unimproved drum printer with that obtained from an improved model. The texts were printed using a drum printer similar to that described in connection with FIG. 1, the improved text, Appendix A(2), being printed by the same drum printer incorporating the solenoid actuated clamp embodiment of the invention. Appendix B illustrates a similar comparison except the texts were printed by unimproved and improved models ofa chain printer such as was described above in connection with FIGS. 4 and 5.

otaaaswaaotzs mrae 123456789 23456'789 Q123456T89012345M89 0123456759Q123456789 0123456759 3346?89 123a567B o123456789 1234567e9 4567a9 7 8 Appendix B, CHAIN PRINTER (1) Without; Clamp 2'? 11 22 33 H4 55 6 77 88 99 CC M @e :2 g: 55 IT i W M xx YY [Z 31 11 22 33 M 55 66 77 88 99 CC M B 1: Illl SS TT Ut; W WW XX YY ZZ H :1 1 12233 0 4 5566 77 88 99 0C MP9 'A l// SSTTUU VVWWXXYY Z2... M 1% ??112233u iE56677E899CC N69 ":zusgttuwm xxvy g2 ??112233 l JE566778S99CCM6 H "lllll/SSTTUUWWHXXYYZZ-..H22:: ??112233 M'5566778899OC## "'QQ//SSTTUUVVWHXXYYZZ--H21:: ??112233ME566778899CC M@ 55TTLL mtxxyy '2'3112233Qflj56778899CC MFH "HH//SSTTUUVVM:XXYYZZ -H21::

(2) With Clamp ??1 1 22334 055 66 77'8899OC #39? Til/SSTTUUVVHWXXYY 22.. H 12:: 1122 33 5566 778899CC M69 ZZI/SSTTLU W M XXYY Z2... .0: :7. ??112233445566778899CCN69:: "MU S TT ,,gz== ??1 1.22334055667788990011889: "/u/SSTTUUVVwMXXYYZZ. 22:: ??112233ME56677E899CC1M6:: "R SSTTU Y Z ,,gz== ??112233445566778899CCH69:: "mw gsrruuvvuuxxwzz ??112233445566778899008368:: "'QQ//55TTUUVVWHXXYYZ ,,gg== ??11223344ES66778899CC 6Q EZIISSTTLL W WXXYY 22... H 22::

What is claimed is:

1. In apparatus for printing on a webbed medium including a row of actuatabl'e impact print hammers each hammer being associated withQadiscrete character position in a print-line, a carrier for continuously displacing a set of raised print characters serially through a print station juxtaposed 'to said row of print hammers, means for intermittently feeding the webbed medium from print line to print line through said print station and for aligning the webbed medium in a predetermined relationship with said row of print hammers, frame structure including a bearing surface defining a path of travel of said webbed medium past said print station, and means for actuating selected ones of said print hammers to impact the webbed medium against predetermined ones of said continuously displacing print characters, the improvement comprising:

a plurality of restraining members disposed adjacent and in the immediate vicinity of said print station and said row of print hammers and arranged in transverse relationship to said bearing surface de-' fining said path of travel of said webbed medium, said restraining members in cooperation with said bearing surface extrinsic thereto being operable to frictionally engage the webbed medium to prevent any and all shiftable movement thereof in the direction of displacement of said print characters caused by said continuous displacement thereof, said prevention of any and all shiftable movement serving to maintain said webbed medium and the impacted areas thereof in proper alignment with said row of print hammers during the printing of each print line, said restraining members being further characterized by their ready installability on the frame structure of existing printing apparatus.

2. The printing apparatus as defined in claim 1 wherein each of said restraining members comprises yieldable force applying means effective for applying a force in a generally perpendicular direction to said extrinsic bearing surface of said frame structure to thereby effectuate said frictional engagement of said webbed medium to prevent said any and all shiftable movement thereof caused by said continuous displacement of said print characters.

3. The printing apparatus as defined by claim 2 wherein each of said plurality of yieldable force applying restraining members is a one-way clutch with a surface composed of material having a high coefficient of friction with respect to the webbed medium, said surface being ridable upon one face of the medium to frictionally prevent said any and all shiftable movement thereof caused by said continuous displacement of said print characters.

4. The printing apparatus as defined in claim 2 wherein each of said plurality of yieldable force applying restraining members is a roller-shaped member rotatable solely in one direction and having a peripheral surface composed of material having a relatively high coefficient of friction with respect to the webbed medium, and wherein each of said members is mounted so as to engage the webbed medium and be rotated thereby in the direction of the feed thereof while at the same time frictionally preventing any and all shiftable movement of the webbed medium caused by said continuous displacement of said print characters.

5. The printing apparatus as defined by claim 2 wherein each of said plurality of yieldable force applying restraining members comprises an actuatable clamp having an engaging pad composed of a material having a high coefficient of friction with respect to the webbed medium, and means for actuating said clamp between intermittent advancing motions of said webbed medium such that said clamp frictionally engages said webbed medium to thereby prevent said any and all shiftable movement thereof caused by said continuous displacement of said print characters.

6. A printing apparatus as defined by claim wherein the engaging pad of each of said actuatable clamps is urged into frictional engagement with the webbed medium by a biasing member, and wherein said pad is retractable from said engagement by the activation of a solenoid operatively associated therewith.

7. Apparatus for printing on a webbed medium, including, in combination:

a print station including a row of actuatable print hammers, each hammer being associated with a discrete character position in a print line, and a cyclically movable carrier operable for continuously displacing a plurality of raised print characters serially past said row of print hammers,

means for intermittently feeding a webbed medium from print line to print line through said print station and for aligning the webbed medium in a predetermined relationship with the discrete character positions represented by said print hammers,

frame structure including a bearing surface defining a path of travel of said webbed medium past said print station,

means for actuating selected ones of said print hammers to impact the webbed medium against selected ones of said continuously displacing print characters and print a line of characters on the webbed medium, and

a plurality of spring-actuated and solenoiddeactuated restraining clamps disposed adjacent and in the immediate vicinity of said print station and said row of print hammers and arranged in transverse relationship to said bearing surface defining said path of travel of said webbed medium, said restraining clamps in cooperation with said bearing surface extrinsic thereto being operable to engage the webbed medium with such frictional force as to prevent any and all shiftable movement thereof in the direction of displacement of said print characters caused by said continuous displacement thereof, said prevention of any and all shiftable movement serving to maintain said webbed medium and the impacted areas thereof in proper alignment with said row of print hammers during the printing of each print line, said restraining clamps being further characterized by their ready installability on the frame structure of said printing apparatus.

8. The printing apparatus as defined in claim 7 wherein during the intermittent feeding of the webbed medium by said intermittent feeding means said webbed medium is alternately advanced and stopped, and wherein said restraining clamps are actuated by spring means in timed relation to said stopping to thereby engage said webbed medium, and deactuated by solenoid means in timed relation to said advancing to thereby disengage said webbed medium. 

1. In apparatus for printing on a webbed medium including a row of actuatable impact print hammers each hammer being associated with a discrete character position in a print line, a carrier for continuously displacing a set of raised print characters serially through a print station juxtaposed to said row of print hammers, means for intermittently feeding the webbed medium from print line to print line through said print station and for aligning the webbed medium in a predetermined relationship with said row of print hammers, frame structure including a bearing surface defining a path of travel of said webbed medium past said print station, and means for actuating selected ones of said print hammers to impact the webbed medium against predetermined ones of said continuously displacing print characters, the improvement comprising: a plurality of restraining members disposed adjacent and in the immediate vicinity of said print station and said row of print hammers and arranged in transverse relationship to said bearing surface defining said path of travel of said webbed medium, said restraining members in cooperation with said bearing surface extrinsic thereto being operable to frictionally engage the webbed medium to prevent any and all shiftable movement thereof in the direction of displacement of said print characters caused by said continuous displacement thereof, said prevention of any and all shiftable movement serving to maintain said webbed medium and the impacted areas thereof in proper alignment with said row of print hammers during the printing of each print liNe, said restraining members being further characterized by their ready installability on the frame structure of existing printing apparatus.
 2. The printing apparatus as defined in claim 1 wherein each of said restraining members comprises yieldable force applying means effective for applying a force in a generally perpendicular direction to said extrinsic bearing surface of said frame structure to thereby effectuate said frictional engagement of said webbed medium to prevent said any and all shiftable movement thereof caused by said continuous displacement of said print characters.
 3. The printing apparatus as defined by claim 2 wherein each of said plurality of yieldable force applying restraining members is a one-way clutch with a surface composed of material having a high coefficient of friction with respect to the webbed medium, said surface being ridable upon one face of the medium to frictionally prevent said any and all shiftable movement thereof caused by said continuous displacement of said print characters.
 4. The printing apparatus as defined in claim 2 wherein each of said plurality of yieldable force applying restraining members is a roller-shaped member rotatable solely in one direction and having a peripheral surface composed of material having a relatively high coefficient of friction with respect to the webbed medium, and wherein each of said members is mounted so as to engage the webbed medium and be rotated thereby in the direction of the feed thereof while at the same time frictionally preventing any and all shiftable movement of the webbed medium caused by said continuous displacement of said print characters.
 5. The printing apparatus as defined by claim 2 wherein each of said plurality of yieldable force applying restraining members comprises an actuatable clamp having an engaging pad composed of a material having a high coefficient of friction with respect to the webbed medium, and means for actuating said clamp between intermittent advancing motions of said webbed medium such that said clamp frictionally engages said webbed medium to thereby prevent said any and all shiftable movement thereof caused by said continuous displacement of said print characters.
 6. A printing apparatus as defined by claim 5 wherein the engaging pad of each of said actuatable clamps is urged into frictional engagement with the webbed medium by a biasing member, and wherein said pad is retractable from said engagement by the activation of a solenoid operatively associated therewith.
 7. Apparatus for printing on a webbed medium, including, in combination: a print station including a row of actuatable print hammers, each hammer being associated with a discrete character position in a print line, and a cyclically movable carrier operable for continuously displacing a plurality of raised print characters serially past said row of print hammers, means for intermittently feeding a webbed medium from print line to print line through said print station and for aligning the webbed medium in a predetermined relationship with the discrete character positions represented by said print hammers, frame structure including a bearing surface defining a path of travel of said webbed medium past said print station, means for actuating selected ones of said print hammers to impact the webbed medium against selected ones of said continuously displacing print characters and print a line of characters on the webbed medium, and a plurality of spring-actuated and solenoid-deactuated restraining clamps disposed adjacent and in the immediate vicinity of said print station and said row of print hammers and arranged in transverse relationship to said bearing surface defining said path of travel of said webbed medium, said restraining clamps in cooperation with said bearing surface extrinsic thereto being operable to engage the webbed medium with such frictional force as to prevent any and all shiftable movement thereof in the direction of displaCement of said print characters caused by said continuous displacement thereof, said prevention of any and all shiftable movement serving to maintain said webbed medium and the impacted areas thereof in proper alignment with said row of print hammers during the printing of each print line, said restraining clamps being further characterized by their ready installability on the frame structure of said printing apparatus.
 8. The printing apparatus as defined in claim 7 wherein during the intermittent feeding of the webbed medium by said intermittent feeding means said webbed medium is alternately advanced and stopped, and wherein said restraining clamps are actuated by spring means in timed relation to said stopping to thereby engage said webbed medium, and deactuated by solenoid means in timed relation to said advancing to thereby disengage said webbed medium. 